The photolithography process is an important technique used in forming selected circuit patterns on a semiconductor wafer. In general, a photoresist film can be deposited onto a substrate wafer during this process and thereafter pattern-exposed to lithographic equipment in order to transcribe a selected circuit pattern. The photoresist is subsequently developed with a developer solution to obtain a resist pattern corresponding to the transcribed pattern. The developer is intended to remove the relatively more soluble areas of photoresist, and leave behind the remaining patterned image which basically serves as a mask for etching multiple semiconductor wafer layers.
In order to form desired patterns on a substrate, the photoresist is processed during the development step with a solution that is applied in a highly controlled manner. Photoresist or resist development is carried out while a semiconductor wafer is rotated at various speeds and stopped intermittently at preselected time intervals for processing. For example, the wafer may be rotated while a developing solution is dispensed onto the wafer from the discharge port of a developer nozzle. A developing solution film may be thus formed which is intended to have a relatively uniform thickness across the surface of the wafer. Both the wafer and the developer film formed thereon are held stationary thereafter for a predetermined time interval so that developing solution remains in intimate contact with the resist-coated wafer in order to develop a light-exposed latent image thereon. Upon completion of this step in the development process, pure water or other rinse solution can be supplied from a washing liquid supplying nozzle onto the surface of the wafer. The pure water or rinse solution may be eventually scattered off by rotating the wafer at a relatively high speed to spin dry the surface of the wafer to complete this stage of wafer processing.
A variety of photoresist and developer materials are typically applied to the wafer using a spin coating technique. Either a photoresist or developer solution is sprayed or otherwise applied on the surface of the wafer and spun on a rotating chuck. The spinning of the wafer distributes the fluid over the surface of the substrate and exerts a shearing force that separates the excess fluid from the wafer thereby providing a thin layer or coating of photoresist, developer or any other type of processing solution. It is often desired to produce a highly uniform layer on the substrate without defects to enable the formation of subsequent layers to be precisely constructed thereon.
A significant problem associated with conventional solution dispense apparatus is their failure to prevent the inadvertent dripping of fluids onto processed wafers or substrates which can lead to defects. Following the spin-coating dispense of solutions using conventional liquid nozzles, residual amounts of fluid such as photoresist are often known to “drip” onto the underlying wafer. Drips of solution may also include certain added impurities residing on the surface of a nozzle body which can further contaminate the wafer. The occurrence of drips may result in uneven resist coating, developing defects, line width defects and shape failures and other undesirable consequences. While some fluid dispense systems today incorporate apparatus such as suck-back valves in an attempt to prevent drips, such equipment tends to add extra complexity in addressing the problem of fluid dripping. The effectiveness of suck-back valves are also limited since the long tubing often used can be compressed which can cause dripping despite use of the valves.
The available equipment and methods used today do not fully meet the high performance demands required by current processing solution dispense applications. There is a need for improved processing solution dispense apparatus and methods which reduce the occurrence of wafer defects and uneven application of a semiconductor processing coatings.